There is known a developer cartridge provided with a gear including a rib-shaped detection portion. This detection portion is engageable with an actuator provided in an image-forming apparatus to perform new product detection or specification detection of the developer cartridge (for example, see Japanese Patent Application Publication no. 2011-203362). In this developer cartridge, the rib-shaped detection portion is rotatable together with the gear and has a narrow end that is configured to press the actuator to pivotally move the actuator. An optical sensor is configured to detect the pivotal movement of the actuator. The optical sensor becomes ON when detecting the pivotal movement of the actuator, while the optical sensor becomes OFF when the narrow end of the detection portion is separated from the actuator.
Here, the optical sensor may be configured to be ON when light is received by a light-receiving element, and to be OFF when light is not received by the light-receiving element, for example. Alternatively, the optical sensor may be configured to become ON when light is not received by the light-receiving element, and become OFF when light is received by the light-receiving element. In the following description, for the sake of convenience, a period of time during which the optical sensor is in its ON state will be referred to as “detection period” and a period of time during which the optical sensor is in its OFF state will be referred to as “non-detection period”.